It is envisaged that not only mobile phones and smartphones but also various things may be connected to the Internet in the future. Various techniques for implementing the Internet of Things (IOT) are presently discussed. As one of these techniques, Dedicated Core Network (DECOR) has been discussed in Rel-13 of Long Term Evolution (LTE) as a control technique for separating general users such as mobile phones and smartphones from Machine-to-Machine (M2M) users such as smart meters and sensors and accommodating respective user equipments in different core networks (CNs) corresponding to device types and/or subscription types.
As illustrated in FIG. 1, in addition to an existing Evolved Packet Core (EPC), an M2M dedicated EPC for M2M users is provided in the DECOR. Upon visiting a base station (evolved NodeB: eNB), user equipment (UE) transmits an Attach/Tracking Area Update (TAU) to the base station. Upon receiving the Attach/TAU, the base station transmits the Attach/TAU to an existing EPC serving as a default CN. Upon receiving the Attach/TAU, the existing EPC transmits an Updated Location Request (ULR) to an IP Service Control Point (IPSCP) or a Home Subscriber Server (HSS). The IPSCP or the HSS returns an Update Location Answer (ULA) to indicate subscription information (user information, an Access Point Name (APN), a UE Usage Type (UE type), or the like) on the user equipment to the existing EPC. The existing EPC determines the UE type from the received subscription information and redirects the Attach/TAU corresponding to the determined UE type. Specifically, the existing EPC determines whether the user equipment is the general user or the M2M user based on the UE type. If the UE type is the general user, the existing EPC accommodates the user equipment. On the other hand, if the UE type is the M2M user, the existing EPC redirects the Attach/TAU to an M2M dedicated EPC (e.g., dedicated CN). In this manner, according to the DECOR, even if lower prioritized M2M terminals are congested, the M2M users are accommodated by the M2M dedicated EPC, which can avoid influence on the general users. Besides, since there are cases where a network function to accommodate the M2M terminals differs from a network function to accommodate the general users, according to the DECOR, the M2M terminals can be allocated to resources for the dedicated core network, and there are some merits where functions and/or resources to be possessed by the dedicated core network can be efficiently introduced.
In the DECOR, a base station redirects a Non Access Stratum (NAS) message to an M2M dedicated EPC based on Dedicated Mobility Management Entity Group Identity (MMEGI). Here, in a conventional CN selection control function where the DECOR is not applied (NAS Node Selection Function: NNSF), upon receiving a connection request from user equipment, the base station selects a Mobility Management Entity (MME) for the user equipment. Specifically, if the user equipment is connecting by an Initial Attach, the base station uses a Globally Unique MME Identity (GUNMEI) or a Selected Public Land Mobile Network (PLMN) included in an RRC Connection Setup Complete to select one MME from MMEs in the relevant network (e.g., PLMN) randomly. On the other hand, if the user equipment is connecting by a Service Request (e.g., restoration from a Preservation state) or a TAU, the base station uses a SAE Temporary Mobile Subscriber Identity (S-TMSI) included in an RRC Connection Request to restore the connection to the relevant MME.
Specifically, in the case where the user equipment attempts the connection by the Service Request or the TAU, as illustrated in FIG. 2, the user equipment first transmits an RRC Connection Request including the S-TMSI to the base station. After returning an RRC Connection Setup, the base station receives an RRC Connection Setup Complete including a Registered MME and a Selected PLMN from the user equipment. Upon receiving the RRC Connection Setup Complete, the base station performs the NNSF and transmits an Initial UE Message to MME #1 corresponding to the Registered MME. Upon receiving the Initial UE Message, the MME #1 exchanges an Initial Context Setup Request or an Initial Context Setup Response with the base station, and an S1 Connection for the relevant UE will be established between the base station and the MME #1.